The principle of the thermal sublimation process consists in transferring the printed image applied to a carrier paper to a suitable substrate by means of high temperature.
The print is produced, for example, using thermal sublimation inks specially provided for this purpose. These inks are applied to the coated carrier paper, for example in the inkjet printing process. On a flatbed or rotary press, the printed image is detached by means of high temperature from the carrier paper, which is in direct contact with the textile or hard substrate. The pigmented inks are converted directly from the solid to the gaseous state (sublimation) and become anchored in the textile or hard substrate.
The sublimation process (vapour phase) is problematic since the separation of carrier paper and substrate can cause ghosting produced by the residual heat. In the transfer process, the use of commercially available carrier papers therefore always results in a certain proportion of production waste, which is associated with high costs.
The adhesive sprays (consisting of styrene acrylate) available on the transfer market provide a remedy but can be only partially applied and, apart from additional costs, result in an increased production outlay. In addition, lower transfer rates have to be expected in certain circumstances as a result of the increased ink retention power of styrene acrylate.
Known synthetic thermoplastics, such as polyvinyl acetate (PVAC), polyethylene (PE), polyamide (PA), polyester (PES), polypropylene (PP), polyvinyl chloride (PVC), polyacrylonitrile (PAN) or polyacrylates, were applied as an additional coating in the case of other transfer papers known on the market, with a function analogous to that of the adhesive spray. However, these synthetic thermoplastics are to be considered as being of low quality, in particular because of the disadvantageous high ink retention power.
The possibility of incorporating synthetic polymers directly into the transfer coating is also unsuccessful since the ink retention power and the printability are very adversely affected by the thermoplastic polymer fraction required in the formulation.
A carrier paper having a coating applied thereon, according to the type mentioned at the outset, is disclosed in US 2005/0186363 A1. The coating applied in the case of this carrier paper preferably consists of carboxymethylcellulose (CMC), alginates and gelatin or mixtures thereof. However, a disadvantage in the case of CMC is that it is not a thermoplastic. Furthermore, starch ethers are used in transfer coatings.
Papers for printing in the inkjet process which are provided with a coating which comprises cellulose constituents are disclosed in EP 1 340 621 A1, EP 0 947 350 A1 and U.S. Pat. No. 4,865,914 A. The coatings are not intended for application in the thermal sublimation process for a textile or a coating of a main substrate.
Papers which are provided with a coating which comprises cellulose constituents are in principle disclosed in EP 1 270 662 A2, EP 1 323 863 A1, U.S. Pat. Nos. 5,080,717 A, 5,654,424 A, 6,030,443 A and US 2005/0191425 A1.